U.S. patent application number 09/839320 was filed with the patent office on 2002-12-05 for battery separator with sulfide-containing inorganic salt.
Invention is credited to Cheiky, Michael, Hago, Wilson.
Application Number | 20020182511 09/839320 |
Document ID | / |
Family ID | 25279414 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020182511 |
Kind Code |
A1 |
Cheiky, Michael ; et
al. |
December 5, 2002 |
Battery separator with sulfide-containing inorganic salt
Abstract
A battery separator for use in a zinc-based battery containing
sulfide ions is employed to minimize copper ion diffusion into the
electrodes by placing a regenerated cellulose separator next to the
copper-containing layer containing low solubility sulfide salts and
precipitating the copper ions.
Inventors: |
Cheiky, Michael; (Santa
Barbara, CA) ; Hago, Wilson; (Ventura, CA) |
Correspondence
Address: |
Marvin E. Jacobs
KOPPEL & JACOBS
Suite 215
2151 Alessandro Drive
Ventura
CA
93001
US
|
Family ID: |
25279414 |
Appl. No.: |
09/839320 |
Filed: |
April 19, 2001 |
Current U.S.
Class: |
429/255 ;
429/206; 429/229; 429/248 |
Current CPC
Class: |
H01M 4/42 20130101; Y02E
60/10 20130101; H01M 50/44 20210101; H01M 4/244 20130101; H01M
10/26 20130101; H01M 50/4295 20210101 |
Class at
Publication: |
429/255 ;
429/248; 429/229; 429/206 |
International
Class: |
H01M 002/16; H01M
010/26; H01M 004/42 |
Claims
1. A separator for use in a zinc alkaline battery containing copper
ions dissolved in an alkaline electrolyte comprising a film of
regenerated cellulose containing a dispersion of sulfide
particles.
2. A separator according to claim 1 in which the salt has a
solubility of less than 1 mg/ml.
3. A separator according to claim 2 in which the sulfide particles
are present in an amount from 2% to 25% by weight.
4. A separator according to claim 3 in which the sulfide salt is
selected from the group consisting of indium sulfide, bismuth
sulfide, zinc sulfide, tin sulfide, lead sulfide, cadmium sulfide
and silver sulfide.
5. A separator according to claim 2 in which the cellulose has a
degree of polymerization from 200 to 1200.
6. A separator according to claim 5 in which the cellulose is
selected from the group consisting of microcrystalline cellulose,
cotton fiber, paper and microgranular cellulose.
7. A separator according to claim 5 in which the film contains 10
to 60 parts by weight of 100 parts cellulose of hydrogen permeable
material.
8. A separator according to claim 7 in which the material forms
hydrogen permeable domains within the film.
9. A separator according to claim 8 in which the material is a
cellulose ether in which the ether groups contain 2 to 8 carbon
atoms.
10. A separator according to claim 9 in which the material is ethyl
cellulose.
11. A zinc alkaline battery containing: a zinc containing anode a
metal containing cathode an alkaline electrolyte containing a
source of copper ions; and a regenerated cellulose separator
dispersed between the anode and cathode containing a low solubility
sulfide for controlling the concentrations of copper ions in the
electrolyte.
12. A battery according to claim 11 in which the source of copper
ions is a regenerated cellulose separator, containing a dispersion
of a copper salt.
Description
TECHNICAL FIELD
[0001] This invention relates to a battery separator for
controlling copper ion diffusion in alkaline rechargeable
batteries.
BACKGROUND OF THE INVENTION
[0002] A zinc based battery presents many challenges for the
battery manufacturer. One of these challenges involves containing
zincate diffusion within the battery. This is a particularly severe
problem because zinc is extremely soluble in the strongly alkaline
environments routinely used as the electrolyte in batteries. The
presence of KZn(OH).sub.x where x=1 to 3 presents a double-edged
sword for the battery designer. The high solubility allows for
rapid current spikes typically unattainable with other battery
systems. On the other hand, this high solubility diffuses zinc ions
in undesired locations within the battery, which upon re-plating
leads to the well-known phenomenon of electrode shape change within
zinc batteries. This shape change entails an agglommeration of the
zinc towards the center of the battery with concomitant depletion
from the edges.
[0003] Additionally, and more seriously, a problem arises from this
high zinc mobility such that there is an accumulation of zinc
dendrites within the separator as the battery cycles. Soluble zinc,
driven by the electric fields of the battery, finds its way through
the pores of the separator. A concentration gradient within the
separator leads, upon zinc re-plating, to dendrite formation. The
dendrites are small tree-like metal formations that are capable of
ripping the separator and prompting a cell short.
[0004] One approach presented disclosed in concurrently filed
co-pending application Ser. No. ______, entitled ______, the
disclosure of which is incorporated herein by reference, is to use
separators impregnated with copper salts. These separators
contribute to a substantial diminution of zinc migration from the
anode to the cathode. This behavior is a result of the copper salts
complexing the cellulose and thus preventing access of zinc to the
pores of the cellulose. A problem with this approach is that copper
tends to leach out from the separator at rates that affect battery
performance. Leached-out copper tends to plate on zinc and modify
the overvoltage potential. It also leaches out and re-plates on
adjacent separators, affecting their ion transport properties.
STATEMENT OF THE PRIOR ART
[0005] Prior art in this area has focused on doping porous
polyolefins with inorganic fillers. Thus, Machi et al in U.S. Pat.
No. 4,273,840 disclose a multi-layer battery separator, wherein a
metal ion binding substance is incorporated into a layer of
synthetic resin that is sandwiched between two layers of synthetic
resin. The first layer and third layers contain a monomer having a
grafted hydrophilic group, and the middle layer with the metal
ion-binding substance is fusion-bonded to the first and third
layers. When the separator is to be used in zinc-silver oxide
batteries, inorganic sulfides such as zinc sulfide, magnesium
sulfide and calcium sulfide are used. All layers to be fused are
preferably composed of polyethylene, polypropylene and other
olefinic thermoplastic resins.
[0006] Ondeck et al in U.S. Pat. No. 5,948,557 disclose a battery
separator made of a microporous material comprised of a linear
polyolefin containing finely divided, substantially water-insoluble
filler particles, such as zinc sulfide, distributed throughout the
matrix. Microporous filaments and fibers are made wettable in U.S.
Pat. No. 5,126,219 by incorporating hygroscopic fillers into the
composition.
[0007] A sulfide additive is added to the alkaline electrolyte in
U.S. Pat. No. 4,078,127. The purpose is to stabilize the divalent
silver oxide (AgO) in the cathode.
STATEMENT OF THE INVENTION
[0008] The present invention provides a separator that diminishes
the availability of soluble copper ions emanating from a
zinc-resistant copper-doped, regenerated cellulose separator.
[0009] In accordance with the invention, a cellulose-based
separator is embedded with an insoluble sulfide salt in a
concentration range of 2 to 25% weight of said separator. The
separator of the invention, when placed next to a copper-containing
separator, minimizes copper ion diffusion into the electrodes by
precipitation of said ions. The present invention relies on the
dispersion of a sufficient amount of sulfide salt in the
regenerated cellulose film as to substantially decrease the
concentration of copper ions in the battery.
[0010] These and many other features and attendant advantages of
the invention will become apparent as the invention becomes better
understood by reference to the following detailed description when
considered in conjunction with the accompanying drawings.
DETAILED DESCRIPTION OF THE DRAWING
[0011] The figure is a cross-sectional view of a zinc alkaline
battery containing a separator according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Referring now to the figure, the battery 10 includes an
anode 12, a cathode 14, a source of copper such as a copper salt
containing separators 18 and a sulfide separator 16 according to
the invention.
[0013] The anode 12 can comprise a high surface area, current
conductor such as a silver screen 22 or expanded metal containing a
layer 24 of anode paste containing particles 25 of Zn/ZnO. The
cathode 14 can also include a silver screen 26 supporting a layer
28 of cathode paste such as silver/silver oxide particles 30
dispersed in a polymer matrix. The zinc dendrite controlling
separator 18 releases copper ions into the alkaline electrolyte
(KOH). The separator 16 in accordance with the invention contains a
dispersion of particles 32 of low solubility metal sulfide. The
sulfide ions react with the copper to form insoluble copper
sulfides.
[0014] This invention concerns minimizing copper ion diffusion
emanating from copper-doped cellulose-based separators. Cellulose
having a degree of polymerization between 200 and 1200 is first
dissolved and an insoluble sulfide salt, of solubility less than 1
mg/ml, is added to said solution in an amount from 2 to 25% weight
of cellulose weight. The separator of the invention prevents
leaching of copper from a zinc-resistant, copper-doped
separator.
[0015] The novel aspect of the present invention is the use of an
insoluble sulfide salt, embedded in a cellulose based separator, to
control copper diffusion in separators. Cellulose remains an
excellent material for use as a separator for alkaline batteries
because of its excellent ion transport properties and low
electrical impedance. It has been used since World War II in the
form of cellophane as the preferred separator material for
zinc-based batteries. Its low electrical resistance of 10
milliohm-in.sup.2 has also led to its favor among battery
manufacturers for use in zinc-based batteries, such as silver-zinc,
zinc-nickel, and zinc manganese dioxide batteries. The separator of
the present invention acts as a copper sink in an alkaline
battery.
[0016] The encapsulation of the active salt is effected as follows.
A solution of cellulose, with a degree of polymerization from 200
to 1200, in the form of, but not limited to, microcrystalline
cellulose, cotton fiber, paper and microgranular cellulose, is
dissolved using a variety of different solvents, including, but not
limited to, LiCl/DMAC, trifluoroacetic acid and N-morpholine
N-oxide. With LiCl/DMAC the applicable range is 3 to 8% by weight
LiCl to DMAC and the applicable range for the percent weight
solution of cellulose to solvent is 1 to 11%. The cellulose
solution may be crosslinked by a variety of methods, in particular
by reacting the cellulose with an alkyl dihalide. A hydrogen
permeable, hydrophobic material, as disclosed in concurrently filed
application Ser. No. _______ (Attorney Docket No. 968-20-003) can
be added at this point.
[0017] The hydrogen permeable material preferably forms hydrogen
permeable domains within the regenerated cellulose film. The
material is preferably soluble in a common solvent to cellulose so
that the domains form on casting. Suitable hydrogen permeable
materials are cellulose ethers in which the ether group contains 2
to 8 carbon atoms and is present in the separator film in an amount
from 10 to 60 parts by weight to 100 parts of cellulose.
[0018] A sulfide salt, with solubility less than 1 mg/ml, is added
to the solution as suspension. Salts with the necessary
requirements include, but are not limited to, indium sulfide,
bismuth sulfide, and zinc sulfide, tin sulfide, lead sulfide,
cadmium sulfide, and silver sulfide. The amount of salt needed is 2
to 25% by weight of starting weight of cellulose.
[0019] The resulting mixture is then cast via conventional methods.
These methods are known to those skilled in the art of membrane
fabrication. They include extrusion of the solution onto a conveyor
belt, casting onto a glass plate with a casting knife or casting
onto a well-leveled glass plate.
[0020] After casting, the resulting solution is coagulated with
conventional techniques, preferably using water as the coagulating
agent. Coagulation may be attained either by exposure to ambient
moisture or by direct application of a water stream to the
resulting solution. The coagulated cellulose material is then
washed to remove the solvent and the LiCl salt. The sulfide salt,
because of its relative insolubility, will remain in the gel. It is
possible to employ alcohols mixed with water, but it is preferable
that they be kept below 50% volume ratio.
[0021] After thorough washing of the resulting gel, the gel may be
dried by any conventional methods, including air-drying,
press-drying, or vacuum-drying.
[0022] Separators built in the manner described above were tested
for ability to contain copper migration in the following manner. A
cavity with two compartments of 20 ml volume each has three
separators dividing the two compartments. The two compartments are
each filled with 20 ml of 50% potassium hydroxide by weight. The
middle separator is impregnated with 150 mg Cu(OH)2 per film. The
left separator does not have any salt at all, while the other
separator has impregnated sulfide salt as in the above example. The
presence of copper in the solution to the left of the left
separator and to the right of the right separator is ascertained
after 24 hours via atomic absorption spectroscopy. Results reported
are in ppm of Cu.
1TABLE 1 FILM TYPE ppm Cu-undoped side ppm Cu-sulfide side
Cellulose A-In.sub.2S.sub.3 3.0 1.2 Cellulose B-In.sub.2S.sub.3 1.9
0.8 Cellulose A-Bi.sub.2S.sub.3 2.7 0.8 Cellulose A-ZnS 3.9 0.8
[0023] It is to be realized that only preferred embodiments of the
invention have been described and that numerous substitutions,
modifications and alterations are permissible without departing
from the spirit and scope of the invention as defined in the
following claims.
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